1. Field of the Invention
The present invention relates to apparatus for, and a method of, heating heat-recoverable articles, and more particularly to such apparatus and such a method for effecting recovery of heat-shrinkable cable closures.
2. Related Art
Heat-recoverable sleeving is often used to protect joins in electrically conducting cables and in optical fiber signalling lines. In use, a sleeve is passed over one end of a cable, for example a cable having multiple pairs of signalling wires and, once jointing of one cable to another cable has been completed, the sleeve is relocated over the joint area, the sleeve spanning the ends of the respective insulating jackets of the cables. Alternatively, after the joint has been formed, a split sleeve is positioned over the jointing area, and is sealed using a hot melt adhesive or other heat-activated sealing material. Heating the sleeve causes it to shrink and grip tightly around the cable jacket and the joint area, thereby effecting water resistance and insulation. Care must be taken during the shrinking operation to ensure that air entrapment is limited.
Thus, for example, if the ends of a sleeve are recovered too rapidly, so that sealing of the sleeve to the insulating cable jackets prevents air from escaping, then the central portion of the sleeve may be prevented from shrinking fully onto the joint area by the entrapped air. Accordingly, skilled operators are employed to effect the shrinking operation, usually by applying a gas torch to the sleeve area, and moving the torch from the center towards the ends.
However, as will be appreciated, many such jointing operations are performed in restricted areas, such as in underground cable chambers, where the effects of combustion products may be dangerous to the operator. Furthermore, the use of a naked flame in such chambers, in which a build up of combustible or explosive gases is possible, should preferably be avoided.
One solution to the above problem has been disclosed in U.S. Pat. No. 5,030,810 which has been made by the present patent. In the aforementioned application, there is disclosed a portable heating device comprising a body forming an elongate enclosure, the interior of which has independently-energizable electrical heating elements, whereby the longitudinal temperature profile within the enclosure, may be controlled. The body comprises two half cylinders hinged on one side. Thus, by placing a sleeved joint in the elongate body, and then energizing the heating elements, the central portion reaches recovery temperature very quickly, while the outer portions reach that temperature more gradually.
It has been found using the heating device disclosed in U.S. Pat. No. 5,030,810 that the quality of the insulation and water resistance of the joint after shrinkage of the heat recoverable sleeve is affected by the temperature inside the enclosure at the time the heating device commences operation. In particular, it has been found that the heating device may produce sleeved joints of poor insulation and water resistance at commencement temperatures below zero degrees fahrenheit.